High-frequency electrical device having gastight envelopes



PEARCE ET AL HIGH-FREQUENCY ELECTRICAL DEVICE HAVING GASTIGHT ENVELOPESMay 12, 1953 Filed Oct. 5, 1946 I I 1 1/ I INVENTORSI ALBERT FREDERICKPEARC E NORMAN CHARLES BARFORD WEW ATTORNEY- Patented May 12, 1953HIGH-FREQUENCY ELECTRICAL DEVICE HAVING GASTIGHT ENVELOPES AlbertFrederick Pearce, Hampton Hills, and Norman Charles Barford, South Bend,England, assignors to Electric & Musical Industries Limited, Hayes,England, a company of Great I Britain- Application October 5, 1946,Serial No. 701,542 In Great Britain June 11, 1943 Section 1, Public Law690, August 8, 1946 Patent expires June 11, 1963 2 Claims.

' This invention relates to high frequency electrical devices havinggas-tight envelopes and particularly, but not exclusively, to electrondischarge devices employing cavity resonators.

It is necessary in devices where an electron beam is required to passthrough a cavity reso nator to ensure that the beam is contained withinan evacuated space from which the atmosphere has to be excluded. It issometimes the practice in these cases to construct the device so thatthe envelope thereof passes through the resonator, part of the resonatorlying within the envelope and part outside the envelope. In such caseselectromagnetic waves can be applied to or abstracted from the resonatorby means of a suitable coupling connected to the part of the resonatorlying outside the envelope. In other cases, however, it is desirable toavoid the use of glass or other insulator inside the resonatorparticularly in cases where the device is intended to operate at highpowers or at very high frequencies. In such cases, in order to providefor the passage of the electromagnetic waves to or from the resonatortwo constructions are sometimes employed. In one of such constructionsthe glass envelope of the device is sealed to the outer walls of theresonator leaving part of the resonator exposed to the atmosphere. Ashort length of waveguide is connected to the exposed part of theresonator to enclose an aperture therein and a glass seal is thenapplied transversely of the waveguide so as to make the resonatorgas-tight, the resonator in this construction thus forming part of theenvelope of the device. In the other construction a concentric linehaving a coupling loop in the resonator is provided which projects fromthe resonator through a vacuum seal. In this case the resonator may betotally enclosed Within an envelope, the resonator thus not forming partof t-he envelope. 1

Owing to the necessity of making vacuum seals either in the length ofwaveguide in the first-mentioned construction or to-the necessity ofproviding a vacuum seal for the concentric line, both of theseconstructions are found to be inconvenient in practice. It has, however,been proposed in British patent specification 'No. 506,881'to arrange acavity resonator in an evacuated envelope andto couple the resonator bya slot to a dielectric waveguide comprising a.

metal tube arranged in the envelope, the metal tube being continuedoutside the envelope. In suclian arrangement diificulties may be experienced owing to the escape of high frequency energy at the discontinuityin the waveguide due to the presence of the envelope. The object of thepresent invention is to provide an improved construction of device inwhich electromagnetic waves can be transmitted through the envelopewithout the necessity of making vacuum-tight seals in the path alongwhich the waves are transmitted and in which the escape of waves such asmight arise in said prior proposal is reduced or avoided.

According to one feature of the invention there is provided a highfrequency electrical device comprising a gas-tight insulating envelopethrough which it is desired to transmit electromagnetic waves of givenfrequency wherein said waves are transmitted by a section of waveguidewithin the envelope and extending to the interior side thereof and by aco-operating section of waveguide on the exterior side of the envelopeand wherein, in order to reduce substantially the escape of said wavesat the discontinuity in the path of said waves due to the presence ofthe envelope between the adjacent ends of said sections, said adjacentends are so dimensioned as to present a low impedance at theoperatingfre quency at said discontinuity.

According to another feature of the invention there is provided a highfrequency electrical device comprising a gas-tight insulating envelopeand a hollow conductor within said envelope adapted to contain highfrequency electromagnetic waves of given frequency, said hollowconductor having an aperture therein which lies adjacent to the interiorside of said envelope and on'the exterior side of said envelope asection of waveguide is provided surrounding said aperture so thatelectromagnetic waves can pass from said aperture to the section ofwaveguide or vice versa and wherein, in order to reduce substantiallythe escape of said waves at the discontinuity in the path of said wavesdue to the presence of the envelope between the aperture and saidsection of waveguide the wall of said hollow conductor surrounding saidaperture andv the adjacent end of said section of waveguide are, sodimensioned as to present a low impedance at the operating frequency atthe discontinuity.

The present invention thus provides means whereby electromagnetic wavescan be transmitted through an insulating envelope without the necessityof providing vacuum-tight seals in the path along which the waves aretransmitted, and moreover, a construction in which the escape of saidwaves due to the presence of the envelope is substantially reduced. Theinvention is especially applicable to devices including within thegas-tight envelope a cavity resonator and in this case an aperture inthe cavity resonator may be surrounded by the length of waveguide.

provided within the envelope or the resonator may be arranged to lieagainst the envelope the section of waveguide on the exterior side ofthe envelope surrounding the aperture in the resonator.

In order that the said invention may be clearly understood and readilycarried into effect, it will now be more fully described with referenceto. the accompanying drawings, in which:

Figure 1 is a cross-sectional view of the invention as applied to anelectron discharge device embodying a hollow resonator,

Figure 2 is a section taken along the line 22 of Figure 1, and

Figure 3 illustrates a modification of the flanges employed in Figures 1and 2 for reducing the escape of energy at the envelope of the device.

As shown in Figures 1 and 2. of the drawings, the. reference numeral 9'indicates a cavity resonator which. is arranged entirely within anenvelope 2 of glass or. other suitable insulating material- It isnecessary to maintain the space within the envelope gas or vacuum-tightand in order to apply to. or abstract high frequency electromagneticwaves from the resonator I without the use of elements which passthrough the envelope 2- giving rise to the necessity of vacuum-tightseals, the resonator I is provided with a length of waveguide 30f anysuitablefcrm in cross-section such as. of rectangular or circular formor of flared. formand which surrounds an aperture 4 inthe resonator IVto or from which. energy can flow. The length. of waveguide 3is suchthat the end thereof remote. from the resonator l abuts against theglass envelope 2. and onv the atmospheric side ct theenvelope 2 aco-operating length of. waveguide '5 is provided arranged coaxially withthe section. 3.. These two sections are not sealed to the envelope andsince the envelope passes between the sections the space within theenvelope is maintained vacuum or gas-tight without the necessity ofseals along. the length of the sections 3: and 5 It is of course notnecessary that thesections 3 and Eabut against the envelope although.the ends of these sections are preferably shaped to conform to theconfiguration of the envelope 2- and are disposed as close thereto aspossible. In order to prevent or reduce the tendency for energy toescape at the discontinuity in the waveguide sections 3. and 5 dueto-the pres ence of the envelope 2 which. of course separates theadjacent-ends of said sections, these ends are dimensioned so as topresent a low impedance to said energy at the operating frequency. Asshown, these ends are provided with flanges 5 and. l respectively, theflanges each being of a width equal to where x is the wavelength of theelectromagnetic waves in the material of which the envelope is made andn is any whole number including zero. Flanges having such dimensionsconstitute in effect a transmission line which is open-circuited at"itsen'd remote from the waveguide sections and appears therefore to beshort-ci-rcuited at the waveguide sections, thus providing said lowimpedance. The thickness of the envelope should of course be kept assmall as possible.

With the construction shown, electromagnetic waves can pass from theresonator through the section 3 through the envelope 2 and into thesection 5 or vice versa withrvery little loss. In an alternativeconstruction the waveguide section 3 can be omitted and the resonator ldisposed close tothe inner surface of the envelope 2, electromagneticwaves then passing from the aperture 4 through the envelope 2 and intothe waveguide section 5. The aperture will then be provided with aflange to co-operate with the flange I of the waveguide section 5 if thewall of the resonator is not (so-extensive with the flange 1.

If it is found that the provision of flanges 6 and 1 shown in Figures 1and 2 do not sufiiciently prevent the? escape of energy, an arrangementas describedin British patent specification No. 562,674 may be employedas shown in Figure 3. In this arrangement the flange I on the waveguidesection 5 is provided with an annular recess 8 the depth of this recessbeing effectively equal to a quarter of the wavelength, in air, of theenergy transmitted through the guide. the recess 8 being, disposed from.the internal wall of theguide at a distance effectively equal to aquarter of a wavelength, in the material of which. the envelope is made,of the energy transmitted through the waveguide, whilst the portion ofthe flange 7 beyond the recess 8' is also arranged to be of the sameradial length. The recess 8 provides in effect a transmission. linewhich is short-circuited at its end; remote from the envelope and.thereriore presents at the envelope a high impedance which is reflectedasa low impedance at the inner surfaces of sections 3 andfi andsocausesthe net impedance at that. point to appear lower than the lowimpedance obtained with the.

construction shown in Figures 1'. and 2. The. portion of the flange ibeyond therecess. serves as a. quarter wave open transmission linepresenting. a low impedance in effective series relation with said highimpedance at the open end of recess 8. The flange 6' on the waveguidesection. 3' is ex.- tended as indicated so. as to be co-extensive with.the periphery of the flange 1 Where standing Waves are present in thewaveguide due for example to mismatching of. the debe understood thatthe invention is not limited in its application to such. devices as itcan be applied to other devices employing cavity resonators, or to otherdevices where it is necessary to. transmit high. frequencyelectromagnetic waves through a vacuum or gas-filled envelope.

What we claim is:

1. A high frequency electrical. device adapted to operate at a givenfrequency comprising two aligned hollow conductors adapted to transmit.electromagnetic waves therethrough, dielectric material separating saidconductors, and. means for presenting a low impedance at the; operatingfrequency between said conductors at: the inner surface thereof, said:means including parallel:

= flanges on the adjacentends of. said. conductors,

one of said flanges. being provided with a. recesshaving a depth equalto. a quarter wavelengthv in air at the operating frequency and havingits. open end located at a distance from said inner surface 1substantially equal to; a quarter wavelength at the operating frequencyin said dielectric material, to provide a high impedance across saidopen end of said recess, the total Width of each of said flanges beingequal to a half wavelength at the operating frequency in said dielectricmaterial, whereby the quarter wave open transmission line section formedby the portions of said flanges outwardly from said recess provides, atsaid open end, a low impedance in series with said recess and the otherof said flanges.

2. A device according to claim 1, wherein said dielectric material is asolid dielectric member in contact with said flanges.

ALBERT FREDERICK PEARCE. NORMAN CHARLES BARFORD.

References Cited in the file of this patent UNITED STATES PATENTS Number

